New series of polyimide (PI) nanocomposites reinforced with three different amounts of multiwalled carbon nanotubes (MWCNT; 0.5, 1, and 3 wt%) were prepared by casting, evaporation and thermal imidization. Homogeneous dispersion of MWCNT in PI matrix was investigated by transmission electron microscopy. The effects of MWCNT on the thermal properties of the PI were investigated by thermogravimetric analysis. The results showed that the thermal stability of the nanocomposites enhanced with the increasing MWCNTs content. The resultant PI=MWCNT nanocomposites were electrically conductive with significant conductivity enhancement at 3 wt% MWCNT, which is favorable for many practical uses.